This invention pertains to a control system which can be used to drive a servo such as an electric motor in self-focusing cameras and the like. More particularly, this invention pertains to a control system of this type which can be used in automatic-focusing systems which use an infra-red transmitter and two infra-red receivers (all fixed on the camera) to determine proper distance to a subject using triangulation.
Inasmuch as electric motors and mechanical elements driven thereby have mechanical inertia, it is possible that a motor which adjusts the focus of a camera objective may, by virtue of inertia, overshoot the position to which the objective is to be adjusted. In the event that such overshoot takes place, it is necessary to reverse the motor and attempt once again to properly adjust the camera objective. However, as focusing criteria are set to increasingly precise values, the likelihood of motor oscillation about the point of critical focus increases. Such oscillation is clearly undesirable since it is desirable to focus a camera objective as quickly as possible so as to avoid user inconvenience.
Moreover, in systems which utilize transmitters and receivers such as those disclosed above, it is possible that when distant subjects are to be photographed, the energy received at the camera site will be insufficient to enable electronic circuitry which is used to drive the motor to detect non-congruence between the outputs of the two receivers which are utilized. This is also clearly undesirable, since without some definite determination of congruence and non-congruence between signals at the receivers, the motor cannot be driven and focusing cannot therefore take place.
It would therefore be desirable to provide a control system of this type which would prevent continuous oscillation of such a servo, and which would further allow the motor to be driven even in the absence of sufficiently strong signals received by the receivers.